What does "data" inside standalone game mean in the Blender License?
If you use an addon to export your game in BGE (Build Game, Game Engine Publishing, etc), the addon will attach your blend file at the end of blenderplayer executable. This way, your blend file is part of the executable, so your blend file must comply the GNU GPL license.

To avoid this, you can keep your blend files external to the executable and simply run them through the Game > Start Game From File actuator, so that your blend files can comply any license you want.

Alternatively, you can run the blenderplayer through command line, with a batch / shell script. I've made this tool using this method, you may find its information useful.